In attempting to fill earth as in land reclaiming or to build structural construction including dikes and roads, on soft, unstable foundation as formed by layer of slimy mud such as industrial waste sludge or unsolid sedimentation heap often referred to recently in Japan as HEDORO; bearing strength of such foundation is often quite insufficient to sustain the load of such superstructure. In fact, the uniaxial compression strength of the soft layer such as the sea-bottom HEDORO is usually less than 1 Kg/cm.sup.2. There is a fear, therefore, of causing sliding rupture or sinking down of such soft foundation if the earth is filled as in land reclaiming or a structural construction is built thereon without improving the strength or solidity of the foundation.
It is conventional, in such attempting to fill earth as in land reclaiming or to build structural construction, thus to generally practice civil or architectural engineering work, on the site of the soft, unstable foundation as mentioned above, either to drive down piles through the soft foundation down to hard, stable substratum or to improve the foundation itself to have sufficient bearing strength. Of these two processes, the former has the drawbacks in that the pile driving causes difficulty when the soft, unstable foundation is very deep and that the process is economically unfavorable when very wide area is to be covered; and thus the latter has wider scope of applicability and is actually used more generally.
Practically, the conventional strengthening constructions for improving the soft, unstable foundation are as follows:
(A) Replacement strengthening construction by replacing the slimy mud material of the soft, unstable foundation with material of good sustaining strength in civil engineering, such for instance as sand.
(B) Compression strengthening construction by compressing the soft, unstable foundation under proper load put thereon.
(C) Sand-draining compression strengthening construction by positively forming draining canals within the soft, unstable foundation as will thus enhance the compression.
(D) Strengthening construction by providing piles of quicklime or the like within the soft, unstable foundation, which pile material is to absorb water, generate heat and cause compression of the foundation. And
(E) Strengthening construction by admixing hardening agent, as cement and other chemical, in the soft, unstable foundation which is thus consolidated as an entirety.
Reviewing these constructions, the one mentioned under (A) has the drawbacks in that much labor, time and cost are required for excavating out the soft, unstable foundation material and substituting the sand therefor and also that the disposal of the excavated slimy mud is a troublesome problem; while those mentioned under (B), (C) and (D) all require quite extensive preparatory works, are low in labor efficiency, are not applicable in the first place when the foundation is under water, and can not guarantee sufficient actual improvement of the bearing strength of the foundation.
In comparison with those construtions (A), (B), (C) and (D), the construction (E) is most simple in its actual working operation, since it requires only to apply the hardening agent into the soft, unstable foundation and to admixing same in situ. It may also here be expected to seal up harmful or noxious material within the consolidated blick, and this may thus be fitted particularly as the construction for strengthening the sea-bottom heap HEDORO. There remain, however, still considerable difficulties as to the labor efficiency and overall economy in actually using this constrution in the conventional manner of hardening the whole entirety of the soft, unstable foundation; because of the great amount of the expensive hardening agent as required in such case and of the accordingly great volume to be covered by the admixing operation. Moreover, it is very difficult to effect uniform admixing throughout the whole entirety, and it resulted in a fear of causing localized sinking down when something is built on the foundation improved in this manner.